The present invention relates to a method and system for the management of the mobility, the management of an idle mode, the registration management (management of attachment and detachment), and the location management (management of tracking area) of a terminal by using a non-access stratum (i.e., network stratum, hereinafter referred to as “NAS”) in a mobile telecommunication network. To this end, the method for the management of mobility, the management of an idle mode, the registration management, and the location management of a terminal by using a NAS protocol, i.e., messages, according to an embodiment of the present invention, includes a terminal (hereinafter, referred to as “UE”) and a mobility management entity (hereinafter, referred to as “MME”), and addresses to a method for efficiently processing security protected NAS messages if received messages are security protected NAS messages, in a case of sending or receiving messages serving as EMM (EPS Mobility Management) messages, i.e., mobility management messages, in a network such as an EPS (Evolved Packet System) of 3GPP, when the terminal performs handover in an active mode, performs location management in an idle mode, and registers to a network, thereby achieving improved efficiency in the mobility management, the position management, and the registration management of a terminal.